The handling of metallurgical plant gases and especially the gases produced in steel-making plants is a well developed art and reference may be made, in this connection, to the following U.S. Pat. Nos. 3,799,520, 4,007,025, 4,055,331, 4,052,042, 4,123,238, 4,145,193, 4,152,123, 4,218,241
as well as to commonly assigned copending applications Ser. No. 198,042 filed Oct. 17, 1980 (now U.S. Pat. No. 4,316,727) and Ser. No. 281,346 filed July 8, 1981. The related application, moreover, describes the recovery of converter gases and certain principles in the operation of a top-blown steel-making converter which are relevant here as well.
In the operation of a top-blown steel-making converter, the refractory-lined upwardly open vessel, which is generally swingable on trunnions about a horizontal axis, can receive a charge of pig iron and scrap. The charge is blown by one or more methods (e.g. top blowing, side blowing or bottom blowing) to decarbonize, desulfurize and dephosphorize the charge.
The blow usually takes place in a number of phases, e.g. a preignition predecarbonization phase in which oxygen or air is blown into or onto the charge and may react in part therewith without strong evolution of carbon oxides, decarbonization phases in which carbon dioxide and carbon monoxide are evolved to a significant degree and post decarbonization phases during which other reactions are carried out to generate still further gaseous components.
In gases which are thus produced are commonly collected by a hood which is lowered to the mouth of the converter when the latter is swung into a more or less upright position for the blow. This hood is connected to the intake side of the blower which draws the evolved gases away from the mouth of the converter.
The gas handling equipment can include gas cleaning units, e.g. scrubbers, cyclones and filters, flaring pipes at which combustible undesirable gases are burnt as they are discharged into the atmosphere and a gas storage vessel in which a portion of the converter gas can be stored for use subsequently, e.g. because of its heat value or to recover valuable components therefrom or for other purposes in the metallurgical process.
In an apparatus or plant of the type with which the present invention is concerned, therefore, a hood can be provided for an oxygen blown converter and can communicate with a blower, flaring stack and storage vessel adapted to collect converter gas which satisfies certain conditions, hereinafter referred to as storage conditions.
The suction side of the blower is connected to the hood and the pressure side of the flaring stack and to the storage vessel, switch-over valves being provided to allow selective discharge of the gases from the blower into the flaring stack and the vessel.
Between the storage stack and the vessel a check valve is provided (to prevent backflow from the vessel to the stack and loss of the stored component), the switch-over device being provided with measuring and control units responsive to the appearance of the storage requirements for switching over between gas flaring and gas storage.
During the storage operation, the flaring stack is cut off and during flaring operations flow to the storage vessel is blocked. The measuring and control devices can include gas analyzers to respond continuously to the composition of converter gas and especially to the oxygen and carbon monoxide contents thereof.
The storage conditions thus can include: an oxygen content less than a maximum permissible level, a carbon monoxide content greater than a minimum permissible level, a storage volume at least sufficient for a blowing period, problem-free operation of the oxygen blowing means (e.g. a top blowing lance), and available storage time greater than the minimum permissible value.
Outside these conditions or under circumstances which do not satisfy them, switch over from flaring to storage does not occur.
In specific terms, the output from the blower is branched and each branch is provided with an open/close or bistable valve having solely the capacity to completely open or completely block a flow cross section.
For flaring operation the open/close or, more simply designated, on/off valve is opened and the on/off valve of the vessel is closed. For storage operation the reverse is the case.
The switchover from flaring operation to storage operation has been found to create difficulties especially when it is not possible to ascertain precisely when, during the blowing process, the switchover from one stage to the other is required. This is because the pressure and volume flow rates of the converter gases fluctuate widely during a blowing period and because it is only possible to feed to the storage vessel converter gas which is at higher pressure than the pressure in the storage vessel.